This invention relates to a radiation curable protective coating composition. More specifically, it relates to a silane free coating composition which, when applied to a substrate and radiation cured, forms a protective, abrasion resistant, weather resistant, ultraviolet light resistant, transparent coating firmly held thereon. In addition, substrates coated with this composition may be tinted and/or dyed. Current markets for such coatings are well established and will expand as the abrasion resistance and weatherability of these coatings is improved.
The use of silanes as major components in abrasion resistant coating compositions is well known. For example, U.S. Pat. No. 3,986,997, issued Oct. 19, 1976, and assigned to Dow Corning Corporation, Midland, MI., and U.S. Pat. Nos. 4,309,319 issued Jan. 5, 1982, and 4,436,851 issued Mar. 13, 1984, and assigned to General Electric Company, Waterford, N.Y., describe thermally cured abrasion resistant coatings formed from mixtures of colloidal silica and alkoxy silanes.
Later, acrylates were introduced into abrasion resistant coating compositions, to allow such compositions to be radiation cured. The introduction of acrylates necessitated the replacement of the alkoxy silanes used in the thermally cured compositions with silanes capable of reacting with acrylates such as acryloxy and/or glycidoxy functional silanes. Such compositions are described, for example, in U.S. Pat. Nos. 4,486,504, issued Dec. 4, 1984, and 4,455,205, issued June 19, 1984, and assigned to General Electric Company, Waterford, N.Y. These patents disclose radiation curable coating compositions prepared from the addition of a multifunctional acrylate monomer to a mixture of acryloxyfunctional silanes, and/or glycidoxy functional silanes and colloidal silica.
Until recently, silanes were thought to be necessary, but costly components of all abrasion resistant coating formulations. The use of silanes, however, has been eliminated where colloidal silica dispersed in an organic solvent is used. Japanese Kokai Patent No. Sho63[1988]-286409 issued Nov. 24, 1988, discloses a method for manufacturing a curable resin composition which contains an .alpha., .beta.-unsaturated carboxylic acid compound and colloidal silica. These coatings, however, have one major drawback. They do not allow aqueous dispersions of colloidal silica to be used. Since aqueous colloidal silicas are, by far, the most common and readily available, a major segment of the colloidal silica market is excluded.
Thus, it would be highly desirable in both an economic and commercial sense if the relatively costly silanes could be eliminated from abrasion resistant coating formulations which contain aqueous dispersions of colloidal silica, while the abrasion resistance of such coating compositions, is maintained or improved.
It is important to note that U.S. Pat. No. 4,348,462, issued Sep. 7, 1982, and assigned to General Electric Company, Waterford, N.Y., states in the Background section of the specification, that,
"[A]lthough it has been known that colloidal silica can be incorporated into heat cured coating systems, the present invention demonstrates for the first time that such colloidal silicas can be utilized to improve the abrasion resistance of ultraviolet light curable coatings. These results are accomplished through the specific combination of colloidal silica with acryloxy functional silanes or water miscible hydroxy acrylates, or preferably both, with catalytic amounts of UV sensitive photoinitiators". PA1 (A) at least one multifunctional acrylate monomer; PA1 (B) an organic compound selected from the group consisting of: PA1 R.sup.2 and R.sup.4 are selected from an alkyl or alkenyl group having 1 to 10 carbons, an aryl, alkaryl, and aralkyl group containing 6 to 10 carbons; any of said groups optionally containing one or more ether oxygen atoms within aliphatic segments thereof and optionally containing one or more functional substituents; PA1 R.sup.3 is selected from the group consisting of hydrogen, a monovalent hydrocarbon radical having from 1 to 6 carbon atoms, and a monovalent hydrocarbon radical having from 1 to 6 carbon atoms and containing at least one hydroxy group; PA1 (C) aqueous dispersion of colloidal silica. PA1 R.sup.2 is selected from an alkyl or alkenyl group having 1 to 10 carbons, an aryl, alkaryl, and aralkyl group containing 6 to 10 carbons; any of said groups optionally containing one or more ether oxygen atoms within aliphatic segments thereof and optionally containing one or more functional substituents; PA1 R.sup.3 is selected from the group consisting of hydrogen, a monovalent hydrocarbon radical having from 1 to 6 carbon atoms, and a monovalent hydrocarbon radical having from 1 to 6 carbon atoms and containing at least one hydroxy group. The exact nature of the organic portion of R.sup.2 is not critical to the operability of this invention, but said organic portion must exclude functionality which would react with either the acryloxy or hydroxy functionality thereon. In other words, the organic portion of the R.sup.2 group serves only as a structure to link the acryloxy functionality thereof with the hydroxy functionality thereof, and is preferably chemically inert. In this regard, the term "inert" defines structures which will not interfere with either the radiation curing of the acryloxy functional group or with the hydroxy functionality. Among the hydroxy acrylates which may be utilized in the present invention are:
No additional references are contained or implied in the aforementioned patent concerning the possibility of a coating composition containing only colloidal silica and water miscible hydroxy acrylates along with photoinitiators. To be anticipatory of a claimed invention, a reference must contain sufficient technical information to describe the claimed invention to a person of ordinary skill in the art to which the claimed invention pertains and to enable such a person to make and use the claimed subject matter, without first having to perform extensive experimentation or make an unobvious contribution. Thus, in the aforementioned patent, there is nothing that would teach how to make a silane free coating composition or even that a silane free abrasion resistant coating composition could exist at all. It is assumed, particularly in view of the fact that it took more than six years from the issuing date of the aforementioned patent, before any claims directed at a silane free abrasion resistant coating composition surfaced, (see Japanese Kokai Patent No. Sho63[1988]-286409 issued Nov. 24, 1988), that persons of ordinary skill in the art, after reading the questionable disclosure contained in U.S. Pat. No. 4,348,462, could not make a silane free abrasion resistant coating composition without first conducting extensive experimentation.
The present invention teaches not only that transparent, abrasion resistant coating compositions containing colloidal silica, water miscible hydroxy acrylates and multifunctional acrylates may be prepared, without the use of silanes, but that other specified organic compounds function in place of, or in conjunction with, water miscible hydroxy acrylates, such as water immiscible hydroxy acrylates and cyclic ethers.